1. Field of the Invention
The present invention relates to a thin-film magnetic head for use in magnetic recording and reproducing apparatus such as magnetic disk apparatus and magnetic tape apparatus and, more particularly, relates to a magnetoresistive head for reproducing recorded information on a record medium by the magnetoresistive effect.
2. Description of the Related Art
Recently, with the advancement in magnetic disk apparatus having smaller sizes and increased recording density, there are demands for implementation of contact recording/reproduction during which the head slider has a reduced flying height, i.e., the slider floats slightly above a record medium or the slider contacts the record medium.
When the velocity of a magnetic disk relative velocity to the head is decreased as the diameter of a magnetic disk is reduced, a conventional magnetic inductive head reproduces a deteriorated output. Therefore, a magnetoresistive head (hereinafter briefly referred to as "MR head") which reproduces an output not dependent on the velocity and provides a high power output even when the disk is rotated at low velocity is desired to be developed.
An MR head supplies a constant sense current to a magnetoresistive element to convert changes in magnitude of a signal magnetic field leaked out from the record track of a record medium into changes in resistance and thereby reproduces information recorded on the record medium as changes in voltage. In conventional MR heads, a magnetoresistive element has been exposed on the surface of the head confronting the medium. Therefore, the recording and reproducing through very low flying height or contacting have been very difficult to realize while using a combination of such a head and a metallic record medium because of a short or discharge occurring in between.
Accordingly, the present inventors proposed in Japanese Laid-open Patent Publication No. Hei 5-114119 a flux-guided type magnetoresistive head in such an arrangement that the magnetoresistive element is not exposed on the surface of the head confronting the medium, and a leakage magnetic field from the medium is guided by a flux guide formed of a soft magnetic material to the magnetoresistive element.
The MR head disclosed in the above laid-open patent publication includes a magnetoresistive element of Ni-Fe set back from the front end face of the head confronting a record medium. The magnetoresistive element is provided with a pair of terminals which define a sense region of the magnetoresistive element therebetween, and a constant sense current is adapted to be supplied from one terminal to the other. The MR head further includes a flux guide having one end thereof exposed in the front end face of the head and the other end magnetically coupled to one end of the magnetoresistive element for guiding a magnetic flux from the record medium to the magnetoresistive element.
The flux guide, magnetoresistive element, and terminals are embedded in a nonmagnetic insulating layer and, upper and lower magnetic shields sandwich the nonmagnetic insulating layer. Further, there is defined a gap between the upper and lower magnetic shields for receiving the magnetic flux from the record medium in the front end face of the head.
The sense region of the magnetoresistive element, defined by the pair of terminals, is formed to be larger than the width of the record track on the record medium. The flux guide has, in its plan view, a trapezoidal form, a home plate form, a triangular form, and the like and arranged to be smaller in width than the sense region of the magnetoresistive element.
In the prior art flux guide type MR head, disclosed in the above laid-open patent publication it has been difficult to control magnetic domains because a flux guide smaller in width is used, it has been difficult to control magnetic domains. Consequently, there has been a problem that the reproduced output and reproduced waveform by the magnetoresistive element tend to vary by the multi-domain activities of the flux guide itself.
The above mentioned problem will be described below in detail with reference to FIG. 29. The magnetoresistive element 2 is magnetically coupled to one end of each of a front flux guide 3 and a back flux guide 4. Since the front flux guide 3 is restricted in its length L (a longer length L makes passage of a signal magnetic field .PHI. difficult), the front flux guide 3 has a form whose length L and width W.sub.1 are virtually equal, i.e., a form close to a square.
Accordingly, the easy axis of magnetization, not shown, becomes unstable, and the signal magnetic field .PHI. incoming in the direction of the arrow in the diagram from the record track of a medium circulates as indicated by the arrows in the diagram in the front flux guide 3 and back flux guide 4 and, thereby, circulating magnetic domains partitioned by magnetic walls 5 are formed in each flux guide.
The phenomenon producing a plurality of circulating magnetic domains partitioned by magnetic walls 5 is called a multiple magnetic domain structure. A magnetic domain structure in which the direction of magnetization is aligned with a definite direction, and no magnetic wall is formed, is called a single magnetic domain structure. Magnetic walls, when applied with an external magnetic field, move to minimize the magnetostatic energy. However, it becomes difficult for the magnetic wall 5 to smoothly move when there are pin holes, projections and the like in the front and rear flux guides 3 and 4, and this causes noise.
Thus, in the MR head disclosed in the above laid-open patent publication, the easy axis of magnetization of the flux guide is unstable. Therefore, a multiple magnetic domain structure is produced in the flux guide and, hence, its response to the signal magnetic field .PHI. from the record medium becomes unstable. As a result, there has been such a difficulty that noises are mixed in the reproduced signal.